One of the most commonly used polymers is polyvinyl chloride (PVC). The rigid properties and high chemical resistance associated with the unplasticized form of this vinyl halide polymer has led to its commercial success in a variety of applications, such as pipes and other plumbing supplies. However, there are many other applications that require PVC to be more flexible, which can be achieved by adding a plasticizer to the PVC. Plasticized PVC finds application in a variety of products, including, for example, films, sheeting, wire and cable coverings.
To date, the majority of PVC plasticizers have been petroleum-derived phthalates, such as dioctyl phthalate and diisononyl phthalate. However, such plasticizers can have a variety of drawbacks, including their price as well as the health and environmental concerns associated with their use.
As a result, there is a need for effective “green” plasticizers for thermoplastics and other polymers that are not based on or contain phthalate plasticizers. Prior art describes the use of alkyl ester of epoxidized vegetable oil as a replacement of phthalate in PVC formulation. These epoxide alkyl esters are produced by various epoxidation processes of bio diesel or by trans-esterfication of epoxidized vegetable oils. Typically most vegetable oils, for example soybean oil or bio diesel obtained from soybean oil, contain about 20% saturate fatty acid esters. These saturated fatty acid esters have no epoxy function to act as an acid scavenger in PVC formulations. In addition, they contribute to the release of fumes during extrusion and after formation of film. They also can migrate to the surface of film causing an oily surface, which is not desirable.
To avoid these problems, the Inventors have surprisingly discovered that improved plasticizer properties can result when the individual components used to make the plasticizer composition are selected and engineered to meet certain criteria. For example, fatty acid esters having a low saturation level can allow the resulting composition to exhibit desired volatility properties. The Inventors have shown that, for example, saturate esters and any other volatile components can be removed by steam stripping or under vacuum fraction distillation after the epoxidation step is completed. Alternatively, they can be removed from bio diesel prior to the epoxidation step under full or partial vacuum to solve the fuming during extrusion and migration to the surface of the film. The Inventors have also discovered that the use of fatty acid esters with reduces saturates, coupled with the use of bio-based oils having high oxirane values, lead to a plasticizer with desirable properties.